1. Technical Field
The disclosure relates to a color correction technique.
2. Description of the Related Art
In chromatology, different kinds of coordinate models are available for analysis of images. For example, a HSI color model is described using three coordinate components: hue, saturation, and intensity. Since the saturation component is a separate component in the HSI color model, a saturation degree of an image may be adjusted directly for achieving a desired color effect.
However, a RGB color model currently adopted as an image storage format needs to be transformed into the HSI color model through a nonlinear transformation process for saturation adjustment. Moreover, after the saturation adjustment, the image of the HSI color model further needs to be nonlinearly inverse-transformed back into the RGB color model. The aforementioned nonlinear transformation processes are relatively complicated and require high circuit costs for implementation.
For reducing calculations, another conventional technique for saturation adjusting involves processing an image of a YCbCr color model that is another commonly used image storage format and that may be linearly transformed into the RGB color model using matrix operations. The YCbCr color model is described using three coordinate components: luma Y, first chroma Cb, and second chroma Cr. Since the first and second chromas Cb, Cr affect a saturation degree of the image, the first and second chromas Cb, Cr are scaled by multiplying with a scaling factor (sy) for adjusting the saturation degree of the image.
Nevertheless, the luma Y in the YCbCr model is not capable of adequately representing an intensity degree of the image, such that the first and second chromas Cb, Cr also contain part of the intensity degree of the image. Thus, when the first and second chromas Cb, Cr are scaled-up for increasing the saturation degree, the intensity degree is also increased simultaneously, so that the image becomes blurry because of over brightness in details. Furthermore, a hue degree of the image deviates because the first and second chromes Cb, Cr in the YCbCr model have a nonlinear transformation relation with the hue component in the HSI model. Thus, the image may not maintain the original hue degree by merely scaling the first and second chromas Cb, Cr.